1. Field of the Invention
The present invention relates to a temperature estimating apparatus for a synchronous motor, and more particularly to a temperature estimating apparatus for a synchronous motor for monitoring voltage between the terminals, etc., by varying d-phase current and estimates winding temperature by estimating counter electromotive voltage and winding resistance.
2. Description of the Related Art
In order to control a synchronous motor, it is important to know the temperature of the synchronous motor. A method for estimating the temperature of a synchronous motor is known which estimates magnet temperature based on the rate of decrease of counter electromotive voltage during the driving of the synchronous motor. The counter electromotive voltage can be calculated by subtracting from the voltage between the terminals a voltage induced by a current. As an alternative method, a method for estimating winding temperature based on the rate of increase of winding resistance is known.
A method for diagnosing a synchronous electric machine is known which measures the speed of the rotor of the synchronous electric machine and the voltages and currents of three phases by using an internal temperature measuring means, determines internal temperatures (coil and magnet temperatures) in the synchronous electric machine by using state observers for the resistance of the coils and the magnetic flux of the magnet, and diagnoses and controls the synchronous electric machine based on the internal temperatures thus determined (for example, refer to Japanese Unexamined Patent Publication No. 2014-230486).
A control apparatus that can reduce the model error of armature interlinkage magnetic flux (for example, refer to Japanese Unexamined Patent Publication No. 2008-92649) is known. A model of q-axis inductance Lq is obtained by using an n-point approximation function, and calculations are performed to determine whether calculational conditions are satisfied or not. Next, an armature flux linkage model is calculated only when a calculation enable signal is output. Next, an armature resistance model is calculated by adding a main circuit cable resistance of a preset model to an armature winding resistance model obtained from an armature winding temperature model. Then, a motor constant estimating unit applies corrective calculation to a motor constant for calculating a rotor magnet pole position model signal and a rotor speed model signal.